A conventional cutting insert comprises grooves (also referred to as “nicks”) which extend so as to separate cutting edges into pieces. For example, Patent Document 1 discloses a cutting insert comprising: an upper surface and a lower surface which are opposed to each other; a peripheral side surface which extends therebetween; a through hole which extends so as to penetrate the upper and lower surfaces; and cutting edges which are formed in an intersecting edge between the upper surface and the peripheral side surface. In this cutting insert, each major cutting edge is provided with three grooves so as to be divided into four portions. Each groove extends in a flank of the peripheral side surface so as to be parallel to an axis of the through hole. These grooves separate each major cutting edge into portions, whereby chips which are to be produced can be made smaller.